This invention relates to a multi-source feedstock distribution system for a plurality of manufacturing processes. In one aspect this invention relates to method and apparatus for controlling the acquisition of fresh feed from a plurality of sources and the distribution of such fresh feed to a plurality of processes, which utilize the feed, in such a manner that feed rate and composition set points are satisfied while maintaining a substantially minimum feed cost.
The present invention was applied to a multi-source feedstock distribution system for an ethylene manufacturing process and will be described in terms of such a system. However, the invention is applicable to the control of any multi-source feedstock distribution system where it is desired to meet feed rate and composition set points while still maintaining a substantially minimum feed cost.
Ethylene processes, which also produce propylene if propane is included in the feed, employ huge volumes of ethane and propane. The feed rate to such plants will often be at least 200,000 pounds per hour.
A number of sources are generally required for the volume of feed required by an ethylene process. Typically, gas from a number of suppliers is stored in storage tanks and gases are withdrawn from the storage tanks as is required to meet the feed requirements of the ethylene process. Also, a plurality of ethylene processes or other processes which utilize propane or ethane are generally fed from the storage tanks.
A plurality of storage tanks are typically utilized. As an example, one storage tank might contain gases having a concentration of about 65 percent ethane, another storage tank might contain gases having a concentration of about 5 percent ethane and a third storage tank might contain gases having a concentration of about 35 percent ethane. Thus, the ethane concentration in the gas from a particular supplier would be determined and this gas would be provided to one of a plurality of storage tanks based on such concentration. The gases in the storage tanks would be mixed and provided as feed to user processes.
With such a large volume of feed it is essential that the feedstock cost be minimized if the plant is to be competitive. This requires an examination of the prices charged by various suppliers and the volume of gas which can be provided at certain prices. In some cases, prices may change if higher volumes are purchased from a particular supplier. Also, contract considerations may require purchasing a certain volume of gas from a particular supplier to avoid penalties.
In the past, it has been typical to minimize feedstock cost and also add feeds as required to meet specified user flow rates. However, this past approach has ignored the resulting feedstock composition. The users have been forced to use whatever feedstock composition is supplied which can result in production losses.
It is thus an object of this invention to provide control of a multi-source feedstock distribution system so that both the feed rate and the composition set points are achieved while also substantially minimizing feed cost.